Thin-film cathode for 3-dimensional microbattery and method for preparing such cathode

ABSTRACT

A method for producing a microbattery including providing a conductive substrate, forming a thin film cathodic layer on at least one surface of the conductive substrate, subsequently forming a thin film electrolyte layer over the cathodic layer and subsequently forming a thin film anodic layer over the electrolyte layer

REFERENCE TO CO-PENDING APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/418,718, filed Oct. 17, 2002 and entitled“THIN-FILM CATHODE FOR 3-DIMENSIONAL MICROBATTERY AND METHOD FORPREPARING SUCH CATHODE”.

FIELD OF THE INVENTION

This invention relates in general to thin-film batteries. Morespecifically, the invention relates to a method for producing thin-filmmicrobatteries having a 3-D structure and cathodes therefor, and themicrobatteries and cathodes obtained by such method.

BACKGROUND OF THE INVENTION

The following references are considered to be pertinent for the purposeof understanding the background of the present invention:

A. Albu-Yaron et al., Thin Solid Films 361-362 (2000) 223-228;

Bates et al., U.S. Pat. No. 5,338,625;

Bates et al., U.S. Pat. No. 5,567,210;

Becker et. al., U.S. Pat. No. 6,214,161;

J. J. Devadasan et al., Journal of Crystal Growth 226 (2001) 67-72;

P. Fragnaud et al., Journal of Power Sources 54 (1995) 362-366;

Laermer et al, U.S. Pat. Nos. 5,498,312 and 6,303,512;

I. Martin-Litas et al., Journal of Power Sources 97-98 (2001), 545-547;

Y. Mild et al., Journal of Power Sources 54 (1995) 508-510;

Nathan et al., U.S. Pat. No. 6,197,450;

Norma R. de Tacconi et al., J. Phys. Chem. (1996), 100, 18234-18239;

E. A. Ponomarev et al., Thin Solid Films 280 (1996) 86-89.

There is a global race to develop miniaturized power sources forapplications including implantable medical devices, remote sensors,miniature transmitters, smart cards, and MEMS(micro-electro-mechanical-system) devices. Thin film lithium batteriesare the leading candidates today, but the existing planar technology haslimitations, such as low energy density.

In thin-film battery technology the battery cell components can beprepared as thin, e.g. 1 micron, sheets built up in layers. The anode,the electrolyte and the cathode are in the form of thin films.Consequently, the anode is located close to the cathode, resulting inhigh current density, high cell efficiency and reduction in the amountof reactants used.

The capacity of a thin-film battery is directly proportional to the areaand thickness of the anode-electrolyte-cathode layers that form it. U.S.Pat. No. 6,197,450 describes a method of increasing the capacity ofthin-film electrochemical devices by increasing the surface-to-volumeratio of the substrate upon which the layered thin-film structure isdeposited. This is accomplished by etching the battery substrate to forman array of variably shaped through-holes. The use of such a substrateincreases the available area for thin film deposition, thus leading toan increase in volume, i.e. capacity of the cell. U.S. Pat. No.6,197,450 also describes a 3-dimensional (3-D) thin-film micro-batterywith layers deposited inside the holes and on both flat surfaces of thesubstrate.

Several studies on cathode materials have been performed to improve theelectrochemical performances of micro-batteries used in microelectronicdevices. Some well-known materials used as the cathode (positiveelectrode) in lithium-ion batteries are LiMn₂O₄, V₂O₅, LiCoO₂ and TiS₂,which have been prepared in the form of a thin-film by variousdeposition methods.

U.S. Pat. Nos. 5,338,625 and 5,567,210 disclose a novel vanadium oxidecathode and use of physical deposition techniques such as rf or dcmagnetron sputtering for the fabrication of thin-film lithium cells,especially thin-film micro-batteries having application as backup orprimary integrated power sources for electronic devices. The batteriesare assembled from solid-state materials, and can be fabricated directlyonto a semiconductor chip, a chip package or a chip carrier.

Others have disclosed methods of preparing different cathode materials.For example, P. Fragnaud et al. disclose a method of preparing athin-film made of LiCoO₂ or LiMn₂O₄ for use as cathodes in secondarylithium batteries. These films were prepared by chemical techniques suchas CVD (chemical vapor deposition) and spray pyrolysis.

Also, I. Martin-Litas has disclosed the preparation of tungstenoxysulfide (WO_(y)S₂) thin films by reactive radio frequency magnetronsputtering.

Preparation of a polycrystalline tungsten disulfide thin film byelectrodeposition on conducting glass plates in galvanostatic route wasdescribed by J. J. Devadasan et al. The obtained film was used forphotoelectrochemical solar cells.

A MoS₂ cathode material for lithium secondary batteries was synthesizedby Y. Miki et al. by using thermal decomposition of (NH₄)₂MoS₄ in ahydrogen gas flow at temperatures from 150 to 300° C. MoS₂ thin filmswere also prepared by electrochemical deposition by reduction oftetrathiomolybdate ions, as described by E. A. Ponomarev and A.Albu-Yaron. According to these publications MoS₂ may be used for variousapplications such as solar cells, solid lubricants and rechargeablebatteries.

Copper sulfide is useful in solar cells and in potentiometric sensordevices. Chemical sulfidisation of copper was described by N. R. deTacconi et al, where the formation of copper sulfide films at copperanodes was accomplished in sulfide containing aqueous NaOH media.

Most of the known methods for the formation of thin films for batteryapplications, including physical methods, such as sputtering and spraypyrolysis, require flat surfaces and are therefore unsuitable for“conformal”, three-dimensional (3-D) structures in which the depositedfilms have to follow a surface's contour. Thus, present depositionmethods are unacceptably disadvantageous for the production of 3-D thinfilm batteries.

SUMMARY OF THE INVENTION

The present invention seeks to provide a method for producing thin-filmmicrobatteries having a 3-D structure and cathodes therefor, and themicrobatteries and cathodes obtained by such method.

There is thus provided in accordance with a preferred embodiment of thepresent invention a method for producing a microbattery includingproviding a conductive substrate, forming a thin film cathodic layer onat least one surface of the conductive substrate, subsequently forming athin film electrolyte layer over the cathodic layer and subsequentlyforming a thin film anodic layer over the electrolyte layer.

Preferably, the forming a cathodic layer includes electrochemicallyforming the cathodic layer.

There is also provided in accordance with another preferred embodimentof the present invention a method for producing a thin film cathodeincluding providing a conductive substrate and electrochemically forminga thin film cathodic layer on at least one surface of the conductivesubstrate.

In accordance with another preferred embodiment of the present inventionthe cathodic layer includes at least one material selected from thegroup consisting of sulfides of a transition metal, oxides of atransition metal and mixtures of the sulfides and the oxides.

In accordance with yet another preferred embodiment of the presentinvention the providing includes providing a non-conductive substrateand forming a conductive layer on at least one surface of thenon-conductive substrate. Preferably, the forming a conductive layerincludes electrolessly depositing a conductive material on the surfaceof the non-conductive substrate. Additionally, the conductive materialincludes at least one material selected from the group consisting of Cu,Ni, Co, Fe, Au, Ag, Pd, Pt and their alloys.

In accordance with another preferred embodiment of the present inventionthe method also includes providing a plurality of cavities in thesubstrate, the cavities having an arbitrary shape and having an aspectratio greater than 1 and depositing the cathodic layer, the electrolytelayer and the anodic layer between the cavities and throughout the innersurfaces of the cavities. Preferably, the cathodic layer, theelectrolyte layer and the anodic layer are continuous. Additionally oralternatively, the cavities have an aspect ratio of between 2 to about50. In accordance with another preferred embodiment of the presentinvention the cavities have a cylindrical geometry.

In accordance with another preferred embodiment of the present inventionthe substrate includes at least one material selected from the groupconsisting of glass, alumina, semiconductor materials, ceramicmaterials, organic polymers, inorganic polymers and glass-epoxycomposites. Additionally, the substrate includes silicon.

In accordance with another preferred embodiment of the present inventionthe cathodic layer includes at least one material selected from thegroup consisting of Cu₂S, MoS₂, Co_(x)S_(y) where x=1-4 and y=1-10,Co_(m)O_(n) where m=1-2 and n=1-3, WS₂, and mixtures thereof.

There is further provided in accordance with another preferredembodiment of the present invention a microbattery including aconductive substrate, a thin film cathodic layer formed on at least onesurface of the conductive substrate, a thin film electrolyte layerformed over the cathodic layer and a thin film anodic layer formed overthe electrolyte layer.

Preferably, the cathodic layer includes an electrochemically formedcathodic layer.

There is yet further provided in accordance with another preferredembodiment of the present invention a thin film cathode including aconductive substrate and a thin film cathodic layer electrochemicallyformed on at least one surface of the conductive substrate.

In accordance with another preferred embodiment of the present inventionthe cathodic layer includes at least one material selected from thegroup consisting of sulfides of a transition metal, oxides of atransition metal and mixtures of the sulfides and the oxides.

In accordance with another preferred embodiment of the present inventionthe conductive substrate includes a non-conductive substrate and aconductive layer formed over at least one surface of the non-conductivesubstrate. Preferably, the conductive layer includes a conductivematerial electrolessly deposited on the surface of the non-conductivesubstrate. Additionally, the conductive layer includes at least onematerial selected from the group consisting of Cu, Ni, Co, Fe, Au, Ag,Pd, Pt and their alloys.

In accordance with another preferred embodiment of the present inventionthe microbattery also includes a plurality of cavities formed in thesubstrate, the cavities having an arbitrary shape and having an aspectratio greater than 1 and the cathodic layer, the electrolyte layer andthe anodic layer are deposited between the cavities and throughout theinner surfaces of the cavities. Additionally, the cathodic layer, theelectrolyte layer and the anodic layer are continuous. Additionally oralternatively, the cavities have an aspect ratio of between 2 to about50. In accordance with another preferred embodiment of the presentinvention the cavities have a cylindrical geometry.

In accordance with another preferred embodiment of the present inventionthe substrate includes at least one material selected from the groupconsisting of glass, alumina, semiconductor materials, ceramicmaterials, organic polymers, inorganic polymers and glass-epoxycomposites. Preferably, the substrate includes silicon.

In accordance with another preferred embodiment of the present inventionthe cathodic layer includes at least one material selected from thegroup consisting of Cu₂S, MoS₂, Co_(x)S_(y) where x=1-4 and y=1-10,CO_(m)O_(n) where m=1-2 and n=1-3, WS₂, and mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified pictorial and sectional illustration of amicrobattery constructed and operative in accordance with a preferredembodiment of the present invention;

FIG. 2 is a SEM of a Cu₂S layer on a flat, silicon substrate coated witha Cu layer;

FIG. 3 is an XRD of Cu₂S on silicon substrate coated with a Cu layer;

FIG. 4 is a graph of charge-discharge curves of a Li/CPE/Cu₂Smicrobattery at 120° C.;

FIG. 5 is a graph of capacity loss of Li/CPE/Cu₂S microbattery;

FIG. 6 is a SEM of MoS₂ on silicon substrate covered with a Ni layer;

FIG. 7 is a graph of charge-discharge curves of a Li/HPE/MoS₂microbattery at room temperature;

FIG. 8 is a graph of capacity loss of a Li/HPE/MoS₂ microbattery;

FIG. 9 is graph of capacity loss of a Li-ion/HPE/MoS₂ microbattery;

FIG. 10 is a graph of charge-discharge curves of Li/CPE/MoS₂microbattery at 120° C.;

FIG. 11 is a graph of capacity loss of a Li/CPE/MoS₂ microbattery; and

FIG. 12 is a graph of charge/discharge curves of a Li-ion/HPE/CoSmicrobattery.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIG. 1, which is a simplified pictorial andsectional illustration of a microbattery constructed and operative inaccordance with a preferred embodiment of the present invention. As seenin FIG. 1, microbattery 100 includes a substrate 102, such as a siliconsubstrate, typically with a thickness of between 300 and 1000 μm.Substrate 102 is preferably provided with a plurality of cavities 104formed therethrough. Cavities 104 are typically formed byphotolithography and deep reactive ion etching (DRIE) as describedfurther hereinbelow. Substrate 102 and cavities 104 are then preferablycoated with a conductive substance to form a thin film current collectorlayer 106, as described hereinbelow. Alternatively, substrate 102 may beformed of a conductive material and the formation of current collectorlayer 106 may be obviated.

The substrate 102 and cavities 104 are subsequently coated with a thinfilm cathodic layer 108. A thin film electrolyte layer 110 and a thinfilm anodic layer 112 are then formed over cathodic layer 108. The thinfilm layers 108, 110 and 112 are typically in the range of 1-10 μmthick, and the cavities are typically in the range of 15-150 μm indiameter. Contacts 114 are typically formed on the current collectorlayer 106 and the anodic layer 112.

In one example of a microbattery constructed and operative in accordancewith the present invention, a 440 μm thick, 3″ diameter, double sidepolished (100) silicon wafer was coated on one side with about 11 μm ofAZ-4562 photoresist. Arrays of square holes with a side dimension of 80μm and inter-hole spacing of about 220 μm were then defined byphotolithography. The sequence of photolithography steps includes:

1. Dehydration baking of wafer after cleaning for 2 min. at atemperature of 110° C. on a hot plate;

2. Dispensing photoresist and spinning at about 1400 RPM for 30 seconds;

3. Solvent removal baking at a temperature of 110° C. for 1 min. on ahot plate;

4. Exposure for between 17 to 22 seconds in a mask aligner;

5. Developing for 4-6 minutes in AZ-726 developer; and

6. Hard baking at a temperature of 110° C. for 3 minutes on the hotplate.

After photolithography, cavities were etched using DRIE in aPlasma-Therm SLR 770 ICP system using a standard Bosch process.Following the formation of cavities 104, the thin film layers 106, 108,110 and 112 were formed.

There are two configurations of the high surface area, 3-dimensional“on-chip” microbattery (3D-MB). In a first configuration, hereinafterreferred to as 3D-MB-1, the cathode material is deposited directly ontothe silicon surface. In the second configuration, hereinafter referredto as 3D-MB-2, as described in U.S. Pat. No. 6,197,450, incorporatedherein by reference, the anode material, such as lithium or carbon, isin electronic contact with the substrate. In this second configuration,an additional layer between the silicon surface and the carbon orlithium anode must be created in order to eliminate intercalation ofLithium ions into the bulk of the silicon at low voltage.

In accordance with a preferred embodiment of the present invention, acopper sulfide thin film cathode is deposited on a silicon substrate. Inone example of this embodiment, the silicon substrate was pretreated insolutions of H₂O(5):H₂O₂(1):NH₄OH(1), H₂O(6):H₂O₂(1):HCl(1) at atemperature of 80-100° C. and in isopropanol, for removing oxides andorganic contaminations. The sample was further wet-etched in a strongbasic solution, rinsed in water and immediately immersed in aPd-containing solution to increase the catalytic activity of the siliconsubstrate surface. Electroless deposition of copper on the siliconsubstrates was carried out in a CuSO₄/HCOH solution and resulted in auniform copper thin film of 500-700 nm. The copper-deposited siliconsamples were immersed into an electrolyte solution containing Cu²⁺ ionsand surfactant materials. Electrochemical copper deposition was carriedout at constant current density of 20-50 mA/cm² for a few minutes. Athicker layer of 5-20 microns of copper was formed on these siliconsamples. This layer serves as the current collector layer. Thecopper-deposited silicon substrates were introduced into an aqueoussolution of polysulfides (a mixture of 10 mM Na₂S, 0.1M NaOH andelemental sulfur) at room temperature and electrooxidized at a constantcurrent of 0.1 mA/cm²-0.5 mA/cm² for a few seconds, forming a thincathode layer, with a thickness of 1-3 microns, of crystalline Cu₂S(verified by XRD) on the copper-coated silicon. The copper electrode wascathodically polarized prior to Cu₂S film growth to reduce any residualoxide layer.

Reference is now made to FIG. 2, which shows a SEM cross-sectional viewof the copper sulfide layer deposited onto a copper coated siliconwafer. The crack between Cu and Cu₂S layers, seen in the lower part ofthis image, is caused by quenching in liquid nitrogen, which was usedfor cross-section cutting of the cathode.

Reference is now made to FIG. 3, which shows the powder XRD analysis ofthe as-deposited films on silicon. The analysis reveals crystallographicpeaks belonging to the deposited Cu layer and Cu₂S.

Reference is now made to FIGS. 4 and 5, which are, respectively, a graphof charge/discharge curves and capacity loss of the Cu2S/compositepolymer electrolyte/lithium battery operating at 120° C. and currentdensity of 50 mA/cm². As seen in FIG. 4, the charge/discharge curve isrepresented by a well-pronounced plateau at about 2.1V. The capacityloss of the battery is about 1.4%/cycle, as seen in FIG. 5.

In accordance with another preferred embodiment of the presentinvention, a thin film cathode of MOS₂ is obtained by cathodicreduction. In one example of this embodiment, a silicon substrate waselectrolessly coated with a thin film of nickel, typically having athickness of 200-300 nm, which serves as the current collector layer.The substrate was then immersed into a solution containing MoS₄ ²⁻ ions,and an ultra thin film of MoS₂, typically hazing a thickness of 300-600nm, was formed by electroreduction of MoS₄ ²⁻ ions on the nickel-coatedsilicon substrate at a constant current density of 10-15 mA/cm².

Reference is now made to FIG. 6, which is a SEM micrograph of across-section of the MoS₂ cathode deposited on a nickel-coated siliconsubstrate. A compact, highly adherent MoS₂ film with a thickness about300 to 600 nm is built. The powder XRD analysis of the as-deposited filmon nickel revealed crystallographic peaks belonging to the nickelsubstrate alone. This may indicate the formation of mainly amorphousMoS₂ deposits.

The formation of the microbattery of the present invention thencomprises the deposition of an ion conductive electrolyte 110 over thealready-deposited cathode layer 108. In the examples describedhereinbelow, the electrolyte was formed by casting a soluble polymermixture directly onto the cathode. In the examples describedhereinbelow, two types of conductive separators were used. The firsttype was a composite polymer electrolyte based on a polyethylene oxide,a lithium salt, such as lithium imide, “triflat” or lithiumbis-oxaloborate, and alumina or silica nanoparticles. The second typewas a so called hybrid gel-polymer electrolyte (HPE) based on ananoporous membrane of polyvinylidene flouride soaked with a lithiumsalt, such as LiPF₆ or Li-Imide, dissolved in an ethylene carbonate:diethylcarbonate (EC:DEC) electrolyte. Solvents, such as diglyme (DG),tetraglyme (TG) and polyethylene glycol dimethyl ether (PEGDME, MW 500),can be used in HPEs as well.

Reference is now made to FIGS. 7-11, which are graphs showing theperformance characteristics of various microbatteries constructed andoperative in accordance with preferred embodiments of the presentinvention. FIG. 7 shows a graph of typical charge-discharge curves of aLi/HPE/MoO_(y)S_(z) cell, with the cathode deposited on a nickelsubstrate. The cell was cycled at room temperature and i_(d)=i_(ch)=10μA/cm². The sloping character of the curves is typical of aninsertion/de-insertion process into a single-phase host materialaccording to the following reaction:MoO_(y)S_(z)+xLi+→Li_(x)MoO_(y)S_(z)

It is to be emphasized that an up to ten-fold increase in the currentdensity did not influence either the shape of the curves (curve b, incomparison to curve a), nor the degradation rate. About 0.8 and 0.6 moleatoms of lithium were reversibly intercalated at low and high currentdensity, respectively. The 1^(st) cycle utilization of the cathodeactive material approached 85%. The Li/HPE/MoO_(y)S_(z) cell ran over1000 successive cycles with 0.05%/cycle capacity loss and 100% Faradaicefficiency, as shown in FIG. 8.

FIG. 9 is a graph showing the capacity loss and charging efficiency of aLi-ion/HPE/MoS₂ cell, with the cathode deposited on a nickel coatedsilicon substrate. The cell was cycled at room temperature and a 100μA/cm² rate. As can be seen in FIG. 9, during more than 1000 reversible100% DOD cycles the degradation rate did not exceed 0.05%/cycle and theFaradaic efficiency was close to 100%.

FIG. 10 shows the charge/discharge of a Li/LiImide₁P(EO)₂₀EC₁ 12% (v/v)Al₂O₃/MoS₂ cell carried out at 125° C. While the same charge-dischargemechanism was expected in this electrochemical system, the degradationdegree in the Li/CPE/MoS₂ cell was 0.5%/cycle, as seen in FIG. 11, whichwas higher than in the HPE-consisting battery. This may be caused bypoor contacts and insufficient ionic mobility in the all-solid-statebattery. It is noteworthy that no self-discharge was detected in all theLi/MoS₂ cells under investigation. Slow overdischarge to 0.2V does notaffect the subsequent cycling behavior of the Li/MoS₂ batteries.

A known method for improving the performance characteristics of abattery is the formation of a protective layer, typically in the form ofa very thin ion-conductive protective film, known as a solid electrolyteinterphase (SEI), over the pyrite particles of the cathode layer. Theformation of the SEI provides protection to the cathode active materialin fully charged and/or fully discharged states and improves theperformance characteristics of the battery. To achieve high performancecharacteristics in the lithium and Li-ion batteries, the SEI must be anelectronic resistor and an ionic conductor. In accordance with anotherembodiment of the present invention, a SEI is built in situ as a solidion-conducting electrolyte in the 3D-microbattery. The SEI iselectrochemically formed by overdischarge of the cell during the firstcycle or during the first few cycles. This procedure may also be carriedout during electrochemical lithiation of graphite in Li-ion batteries.

For a lithium battery, a metallic lithium electrode was used as theanode material. For lithium-ion applications, additional casting oflithiated graphite particles with polymer used as a binder is needed. Inaccordance with another embodiment of the present invention, amicrobattery is formed by depositing an anode layer directly on thecurrent collector layer. In this embodiment, the anode is formed byelectrochemical deposition of an anode material, such as Sn_(x)Sb_(y),onto the first layer of the current collector, or by chemical vapordeposition of a carbonaceous precursor on nickel-deposited silicon,where the nickel coating acts as a catalyst. This is followed bysuccessive formation of a soft carbon layer that serves as the anode forlithium-ion batteries.

For the three-dimensional batteries of both the 3D-MB-1 structure, inwhich the cathode material is deposited directly onto the substratesurface, and the 3D-MB-2 structure, where the anode material is inelectronic contact with the substrate, the filling of cylindrical holesof the perforated silicon by HPE and lithiated graphite can be performedby spinning and/or vacuum pooling.

The following are additional examples of microbatteries withelectrochemically deposited cathodes, constructed and operative inaccordance with further embodiments of the present invention, and theirperformance. One example is a planar thin film Li/copper sulfide-onsilicon battery with a solid polymer and gel electrolyte was cycled at120° C. and at room temperature. The degree of degradation of both cellswas in the range of 1.5-2.5%/cycle. The capacity loss of a Li/solidpolymer electrolyte/mixed cobalt cathode cell was about 3%/cycle. Inanother example, a planar 1 cm² Li/gel polymer electrolyte/molybdenumsulfide cell went through over 1000 reversible cycles with a capacityloss of less than 0.1%/cycle at room temperature. In a further example,a 3D Li-ion/HPE/MoS₂ battery went over 50 reversible cycles withcapacity loss of about 0.5%/cycle.

Microbatteries routinely go more than 100 cycles. The thin-film Cu₂S/Libattery can operate both at room temperature and at a temperature of120° C. The cell delivers a rechargeable capacity of 160 mAh/g with aflat potential plateau at ca. 1.6V vs. Li/Li⁺.

EXAMPLE 1

A secondary electrochemical cell, consisting of a lithium anode, ahybrid polymer electrolyte and a MoS₂ cathode on a silicon substrate,was assembled.

To remove organic and metallic residues, the silicon substrate wasimmersed in a solution of H₂O₂:NH₄OH for 5 min at 70° C. and washed indeionized water with successive immersion into a H₂O₂:HCl mixture foranother 5 min. After rinsing in deionized water, the substrate wasetched in a NH₄F:HF solution for 2 min. The surface activation wasaccomplished in a PdCl₂:HCl:HF:CH₃COOH solution at room temperature for2 min.

A 0.3 μm thick cathode was prepared by reduction of MoS₄ ²⁻ ions on anickel coated silicon substrate at a constant current density of 10-15mA/cm². The nickel deposition was carried out in a NiSO₄:NaH₂PO₂:EDTA(or CH₃COONa) solution with pH of 4 and at an elevated temperature of90° C. for a few minutes. The thickness of the nickel deposited is afunction of time and can be varied.

The deposition of the MoS₂ was carried out using an aqueous solution of0.05M tetrathiomolybdate. A potassium chloride (0.1 M) electrolyte wasthe supporting electrolyte. The electrodeposition was carried out atroom temperature using a constant current density of 10 mA/cm² for 4min. The deposited samples were thoroughly rinsed in deionized water andvacuum-dried at an elevated temperature.

SEM micrographs reveal that the films deposited at room temperature arefairly continuous without visible cracks. EDS measurements showed 1:2Mo:S ratio. XPS data supported this composition. The films were X-raytransparent, indicating an amorphous structure of MoS₂.

The preferred polymer for the hybrid polymer electrolyte (HPE) is acommercially available PVDF-2801 copolymer (Kynar). The PVDF powder wasdissolved in high-purity cyclopentanone (Aldrich). Fumed silica 130(Degussa) and propylene carbonate (PC, Merck), were added and themixture was stirred at room temperature for about 24 hours to get ahomogeneous slurry. After complete dissolution, the slurry was cast onthe Teflon support and spread with the use of the doctor-bladetechnique. To prevent surface irregularities, the film was then coveredwith a box with holes to allow a slow evaporation of the cyclopentanone.After complete evaporation of the cyclopentanone, a 13 mm diameter discwas cut from the polymer membrane. The disc was then soaked in aLiImide-based electrolyte for 48 hours. At least three fresh portions ofelectrolyte were used for each soaking to ensure a complete exchange ofthe PC by the electrolyte. LiImide-ethylene carbonate (EC):dimethylcarbonate (DMC) 1:1 (v/v) based electrolytes were stored in a glove boxwith Li chips.

The Li/HPE/MoS₂ cells were cycled at room temperature using a Maccorseries 2000 battery test system. The voltage cut-off was 1.3 to 2.4 V,and the charge/discharge current density was 10-100 μA/cm². TheLi/HPE/MoS₂ cell delivered above 20 μAh per cycle at 100 μA/cm² (FIG. 8)for over 1000 reversible cycles with the capacity fade of 0.05%/cycle.The Faradaic efficiency was close to 100%.

EXAMPLE 2

A Li/composite polymer electrolyte (CPE)/MoS₂ battery was assembled. Thecathode was prepared as in Example 1.

A 50 μm thick film composite polymer electrolyte with a composition ofLiImide₁ P(EO)₂₀ EC₁ 9% v/v Al₂O₃ was prepared from 45 mg LiImide, 300mg P(EO), 30 mg EC and 100 mg Al₂O₃.

Poly(ethylene oxide) (P(EO)) was purchased from Aldrich, (averagemolecular weight 5×10⁶) and was vacuum dried at a temperature of 45 to50° C. for about 24 hours. A polymer slurry was prepared by dispersingknown quantities of P(EO), LiImide, and ethylene carbonate (EC) inanalytical grade acetonitrile, together with the required amount of aninorganic filler, such as Al₂O₃ (Buehler) with an average diameter ofabout 150 A. To ensure the formation of a homogeneous suspension, anultrasonic bath or high-speed homogenizer was used. The suspension wasstirred for about 24 hours before the PE films were cast on the finepolished Teflon support (64 cm² area). The solvent was allowed toevaporate slowly and then the films were vacuum dried at 120° C. for atleast 5 hours. The final thickness of the solvent-free PE films wasbetween 30 to 50 μm thick.

The Li/composite polymer electrolyte (CPE)/MoS₂ battery was cycled at atemperature of 120° C. and a current density of 50 mA/cm². The voltagecutoff on discharge was 1.1 V. The voltage cutoff on charge was 2.2 V(FIG. 10). The cell went through over 40 reversible cycles (100% DOD),and the degree of degradation did not exceed 0.5%/cycle (FIG. 11).

EXAMPLE 3

A Li/CPE/Cu₂S cell with a 1 μm thick film composite cathode was preparedand assembled as described in Example 1, using the following materials:33 mg LiI, 216 mg P(EO), 41 mg EC, 100 mg Al₂O₃. A 100% dense Cu₂Scathode was prepared by anodic oxidation of a metallic copper layerelectrodeposited on the electroless copper. The silicon substrate waspretreated, in solutions of H₂O(5):H₂O₂(1):NH₄OH(1),H₂O(6):H₂O₂(1):HCl(1) at temperatures of 80-100° C. and in isopropanol,to remove oxides and organic contaminations. The sample was furtherwet-etched in a strong basic solution, then rinsed in water andimmediately immersed in a Pd-containing solution to increase thecatalytic activity of the silicon substrate surface. The solution forelectroless copper deposition consisted of (g/L): 10-15 CuSO₄x5H₂O,10-15 NaOH, 2-3 NiCl₂xH₂O, 0.001 Na₂S₂O₈, 15-25 mL/L HCOH (37%).

The electrolyte for copper electrodeposition contained (g/L): 200-250CuSO₄x5H₂O and 50-60 H₂SO₄. The electrodeposition was performed at roomtemperature and a current density of 50 mA/cm² for 8 min. The copperlayer thus formed was electrooxidised in an aqueous solution ofpolysulfides, consisting of a mixture of 10 mM Na₂S, 0.1M NaOH andelemental sulfur, at a constant current of 0.1 mA/cm²-0.5 mA/cm² for afew seconds. A SEM micrograph of the silicon-copper-copper sulfidelayers is shown in FIG. 2. XRD data affirming the obtaining of a Cu₂Scompound is shown in FIG. 3.

The Li/CPE/Cu₂S cell went through over 50 reversible cycles, and thedegree of degradation did not exceed 1.5%/cycle, as seen in FIGS. 4 and5.

EXAMPLE 4

A Li/HPE/Cu₂S cell with a 1 μm thick film cathode was prepared andassembled as described in Examples 2 and 3. The cell went through over120 reversible cycles (100% DOD), with the degree of degradation being0.8%/cycle.

EXAMPLE 5

A Li/CPE/WS₂ cell with a 0.4 μm thick film composite cathode wasprepared as described in Example 2. The cell went through over 135reversible cycles (100% DOD), and the degree of degradation did notexceed 0.2%/cycle.

EXAMPLE 6

A Li/CPE/Cu₂S cell with a 2 μm thick film composite cathode with a Li₂S₆to LiI ratio of 1:0.25 was assembled as described in Example 3. TheLi/CPE/Cu₂S cell was cycled for over 40 (100% DOD) cycles.

EXAMPLE 7

A Li/CPE/Co_(x)S_(y) cell with a 0.3 μm thick film composite cathode wasassembled as described in Example 3. A 100% dense Co_(x)S_(y) cathodewas prepared by electrochemical oxidation of metallic Co in the solutionof polysulfides. The Li/CPE/Co_(x)S_(y) cell was cycled for over 30(100% DOD) cycles (FIG. 12).

EXAMPLE 8

A lithium-ion/MoS₂ cell with a 0.5 μm thick film cathode and a hybridpolymer electrolyte was prepared according to the procedure ofExample 1. The HPE was formed, by casting, on a cathode layer depositedon a silicon substrate. The lithiation of graphite powder was carriedout as follows:

1. A polymer binder (polystyrene) was dissolved in toluene. Afterdissolution, a graphite powder, with an average particle size of a fewμm, was added to the mixture. The resulting slurry was spread on acopper current collector by doctor blade.

2. This electrode was vacuum dried and assembled with lithium andion-conductive separator (Celgard soaked in 1M LiPF6 EC:DEC 1:1 v/v) incells.

3. After a few successive cycles, the cells were disassembled and thelithiated electrode was rinsed in DMC and vacuum dried.

The lithiated graphite electrodes were used as anodes in Li-ion/HPE/MoS₂on-silicon battery. The battery was reversibly charged-discharged forover 1000 cycles with capacity loss of 0.06%/cycle. The Faradaicefficiency was close to 100%. The battery delivered about 10 μAh percycle (FIG. 9).

EXAMPLE 9

A 3D-lithium-ion/MoS₂ cell, with a 0.3 μm thick film cathode and ahybrid polymer electrolyte, was prepared according to the procedures ofExamples 1 and 8. The electrodeposition was performed in a 0.05Mtetrathiomolybdate electrolyte. Lithiated graphite (see Example 8) waspeeled from the copper electrode and introduced into a toluene solution.A few hours of stirring produced a homogenous mixture of lithiatedgraphite and binder in toluene. The cylindrical holes of the perforatedsilicon were filled with HPE and lithiated graphite by spinning. Thebattery was reversibly charged-discharged for 50 cycles and delivered 35μAh per cycle. The Faradaic efficiency was close to 100%.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove as well as variations and modifications whichwould occur to persons skilled in the art upon reading the specificationand which are not in the prior art.

1. A method for producing a microbattery comprising: providing aconductive substrate; forming a thin film cathodic layer on at least onesurface of said conductive substrate; subsequently forming a thin filmelectrolyte layer over said cathodic layer; and subsequently forming athin film anodic layer over said electrolyte layer.
 2. A methodaccording to claim 1 and wherein said forming a cathodic layer compriseselectrochemically forming said cathodic layer.
 3. A method according toclaim 1 and wherein said cathodic layer comprises at least one materialselected from the group consisting of sulfides of a transition metal,oxides of a transition metal and mixtures of said sulfides and saidoxides.
 4. A method according to claim 1 and wherein said providingcomprises: providing a non-conductive substrate; and forming aconductive layer on at least one surface of said non-conductivesubstrate.
 5. A method according to claim 4 and wherein said forming aconductive layer comprises electrolessly depositing a conductivematerial on said surface of said non-conductive substrate.
 6. A methodaccording to claim 5 and wherein said conductive material comprises atleast one material selected from the group consisting of Cu, Ni, Co, Fe,Au, Ag, Pd, Pt and their alloys.
 7. A method according to claim 1 andalso comprising: providing a plurality of cavities in said substrate,said cavities having an arbitrary shape and having an aspect ratiogreater than 1; and depositing said cathodic layer, said electrolytelayer and said anodic layer between said cavities and throughout theinner surfaces of said cavities.
 8. A method according to claim 7 andwherein said cathodic layer, said electrolyte layer and said anodiclayer are continuous.
 9. A method according to claim 7 and wherein saidcavities have an aspect ratio of between 2 to about
 50. 10. A methodaccording to claim 7 and wherein said cavities have a cylindricalgeometry.
 11. A method according to claim 1 and wherein said substratecomprises at least one material selected from the group consisting ofglass, alumina, semiconductor materials, ceramic materials, organicpolymers, inorganic polymers and glass-epoxy composites.
 12. A methodaccording to claim 1 and wherein said substrate comprises silicon.
 13. Amethod according to claim 1 and wherein said cathodic layer comprises atleast one material selected from the group consisting of Cu₂S, MoS₂,CO_(x)S_(y) where x=1-4 and y=1-10, Co_(m)O_(n) where m=1-2 and n=1-3,WS₂, and mixtures thereof.
 14. A method for producing a thin filmcathode comprising: providing a conductive substrate; andelectrochemically forming a thin film cathodic layer on at least onesurface of said conductive substrate.
 15. A method according to claim 14and wherein said cathodic layer comprises at least one material selectedfrom the group consisting of sulfides of a transition metal, oxides of atransition metal and mixtures of said sulfides and said oxides.
 16. Amethod according to claim 14 and wherein said providing comprises:providing a non-conductive substrate; and forming a conductive layer onat least one surface of said non-conductive substrate.
 17. A methodaccording to claim 16 and wherein said forming a conductive layercomprises electrolessly depositing a conductive material on said surfaceof said non-conductive substrate.
 18. A method according to claim 17 andwherein said conductive material comprises at least one materialselected from the group consisting of Cu, Ni, Co, Fe, Au, Ag, Pd, Pt andtheir alloys.
 19. A method according to claim 14 and also comprising:providing a plurality of cavities in said substrate, said cavitieshaving an arbitrary shape and having an aspect ratio greater than 1; anddepositing said cathodic layer between said cavities and throughout theinner surfaces of said cavities.
 20. A method according to claim 19 andwherein said cathodic layer is continuous.
 21. A method according toclaim 19, wherein said cavities have an aspect ratio of between 2 toabout
 50. 22. A method according to claim 19, wherein said cavities havea cylindrical geometry.
 23. A method according to claim 14 wherein saidsubstrate comprises at least one material selected from the groupconsisting of glass, alumina, semiconductor materials, ceramicmaterials, organic polymers, inorganic polymers and glass-epoxycomposites.
 24. A method according to claim 14, wherein said substratecomprises silicon.
 25. A method according to claim 14, wherein saidcathodic layer comprises at least one material selected from the groupconsisting of Cu₂S, MoS₂, CO_(x)S_(y) where x=1-4 and y=1-10,CO_(m)O_(n) where m=1-2 and n=1-3, WS₂, and mixtures thereof.
 26. Amicrobattery comprising: a conductive substrate; a thin film cathodiclayer formed on at least one surface of said conductive substrate; athin film electrolyte layer formed over said cathodic layer; and a thinfilm anodic layer formed over said electrolyte layer.
 27. A microbatteryaccording to claim 26 and wherein said cathodic layer comprises anelectrochemically formed cathodic layer.
 28. A microbattery according toclaim 26 and wherein said cathodic layer comprises at least one materialselected from the group consisting of sulfides of a transition metal,oxides of a transition metal and mixtures of said sulfides and saidoxides.
 29. A microbattery according to claim 26 and wherein saidconductive substrate comprises: a non-conductive substrate; and aconductive layer formed over at least one surface of said non-conductivesubstrate.
 30. A microbattery according to claim 29 and wherein saidconductive layer comprises a conductive material electrolessly depositedon said surface of said non-conductive substrate.
 31. A microbatteryaccording to claim 29, wherein said conductive layer comprises at leastone material selected from the group consisting of Cu, Ni, Co, Fe, Au,Ag, Pd, Pt and their alloys.
 32. A microbattery according to claim 26and also comprising a plurality of cavities formed in said substrate,said cavities having an arbitrary shape and having an aspect ratiogreater than 1; and wherein said cathodic layer, said electrolyte layerand said anodic layer are deposited between said cavities and throughoutthe inner surfaces of said cavities.
 33. A microbattery according toclaim 32 and wherein said cathodic layer, said electrolyte layer andsaid anodic layer are continuous.
 34. A microbattery according to claim32, wherein said cavities have an aspect ratio of between 2 to about 50.35. A microbattery according to claim 32, wherein said cavities have acylindrical geometry.
 36. A microbattery according to claim 26 andwherein said substrate comprises at least one material selected from thegroup consisting of glass, alumina, semiconductor materials, ceramicmaterials, organic polymers, inorganic polymers and glass-epoxycomposites.
 37. A microbattery according to claim 26, wherein saidsubstrate comprises silicon.
 38. A microbattery according to claim 26,wherein said cathodic layer comprises at least one material selectedfrom the group consisting of Cu₂S, MOS₂, Co_(x)S_(y) where x=1-4 andy=1-10, Co_(m)O_(n) where m=1-2 and n=1-3, WS₂, and mixtures thereof.39. A thin film cathode comprising: a conductive substrate; and a thinfilm cathodic layer electrochemically formed on at least one surface ofsaid conductive substrate.
 40. A thin film cathode according to claim 39and wherein said cathodic layer comprises at least one material selectedfrom the group consisting of sulfides of a transition metal, oxides of atransition metal and mixtures of said sulfides and said oxides.
 41. Athin film cathode according to claim 39 and wherein said conductivesubstrate comprises: a non-conductive substrate; and a conductive layerformed over at least one surface of said non-conductive substrate.
 42. Athin film cathode according to claim 41 and wherein said conductivelayer comprises a conductive material electrolessly deposited on saidsurface of said non-conductive substrate.
 43. A thin film cathodeaccording to claim 41 and wherein said conductive layer comprises atleast one material selected from the group consisting of Cu, Ni, Co, Fe,Au, Ag, Pd, Pt and their alloys.
 44. A thin film cathode according toclaim 39 and also comprising a plurality of cavities formed in saidsubstrate, said cavities having an arbitrary shape and having an aspectratio greater than 1; and wherein said cathodic layer is depositedbetween said cavities and throughout the inner surfaces of saidcavities.
 45. A thin film cathode according to claim 44 and wherein saidcathodic layer is continuous.
 46. A thin film cathode according to claim44, wherein said cavities have an aspect ratio of between 2 to about 50.47. A thin film cathode according to claim 44, wherein said cavitieshave a cylindrical geometry.
 48. A thin film cathode according to claim39 wherein said substrate comprises at least one material selected fromthe group consisting of glass, alumina, semiconductor materials, ceramicmaterials, organic polymers, inorganic polymers and glass-epoxycomposites.
 49. A thin film cathode according to claim 39, wherein saidsubstrate comprises silicon.
 50. A thin film cathode according to claim39, wherein said cathodic layer comprises at least one material selectedfrom the group consisting of Cu₂S, MoS₂, CO_(x)S_(y) where x=1-4 andy=1-10, Co_(m)O_(n) where m=1-2 and n=1-3, WS₂, and mixtures thereof.